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Board Saver for Use With Developmental FPGAs

Wednesday, 26 August 2009

A printed-circuit board is protected against repeated soldering
and unsoldering.

A device denoted a board saver has
been developed as a means of reducing
wear and tear of a printed-circuit
board onto which an antifuse field-programmable
gate array (FPGA) is to
be eventually soldered permanently
after a number of design iterations.
The need for the board saver or a similar
device arises because (1) antifuse- FPGA design iterations are common
and (2) repeated soldering and unsoldering
of FPGAs on the printed-circuit
board to accommodate design
iterations can wear out the printed-circuit
board. The board saver is basically
a solderable/unsolderable FPGA
receptacle that is installed temporarily
on the printed-circuit board.

The board saver is, more specifically,
a smaller, square-ring-shaped, printed-circuit
board (see figure) that contains
half via holes — one for each contact
pad — along its periphery. As initially
fabricated, the board saver is a wider
ring containing full via holes, but then it
is milled along its outer edges, cutting
the via holes in half and laterally exposing
their interiors. The board saver is
positioned in registration with the designated
FPGA footprint and each via
hole is soldered to the outer portion of
the corresponding FPGA contact pad
on the first-mentioned printed-circuit
board. The via-hole/contact joints can
be inspected visually and can be easily
unsoldered later.

The square hole in the middle of the
board saver is sized to accommodate
the FPGA, and the thickness of the
board saver is the same as that of the
FPGA. Hence, when a non-final FPGA
is placed in the square hole, the combination
of the non-final FPGA and the
board saver occupy no more area and
thickness than would a final FPGA soldered
directly into its designated position
on the first-mentioned circuit
board. The contact leads of a non-final
FPGA are not bent and are soldered, at
the top of the board saver, to the corresponding
via holes. A non-final FPGA
can readily be unsoldered from the
board saver and replaced by another
one. Once the final FPGA design has been determined, the board saver can
be unsoldered from the contact pads
on the first-mentioned printed-circuit
board and replaced by the final FPGA.

This work was done by Andrew Berkun
of Caltech for NASA’s Jet Propulsion
Laboratory. NPO-44745

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